Mobile communication method

ABSTRACT

A radio terminal UE according to one embodiment includes a radio communication unit  210  configured to receive a plurality of parameters including a first parameter for high-speed movement and a second parameter for non-high-speed movement as parameters for processing for switching to a neighboring base station from a base station connected to the radio terminal, and a controller  260  configured to acquire movement speed information indicating a movement speed of the radio terminal and to select a parameter corresponding to the movement speed information. The first parameter is configured to inhibit processing for switching to a Pico base station PeNB which is included in the neighboring base stations.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication No. 61/471,304 filed on Apr. 4, 2011; the entire contents ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a mobile communication method, a basestation, a radio terminal, and a low-power base station, which are usedfor a heterogeneous network.

2. Description of the Related Art

As a next-generation mobile communication system achievingcommunications with a higher-speed and larger-capacity, standardizationsof LTE (Long Term Evolution) Advanced are in progress by the 3GPP (3rdGeneration Partnership Project) which is a standardization organizationthereof.

A network of the LTE Advanced under consideration for provision is aheterogeneous network in which a low-power base station with a smallcell (a service area range) is effectively deployed in addition to ahigh-power base station (so-called, a macro base station). Thislow-power base station includes a so-called pico base station, femtobase station, relay node, and the like.

In the heterogeneous network, a load of a high-power base station can bedistributed to a low power base station, so that a service qualityprovided to a radio terminal can be improved. However, including cellswith different sizes, the heterogeneous network necessitates atechnology that can improve a service quality for a moving radioterminal (see, 3GPP contributed article, RP-110438, New work itemproposal for Hetnet Mobility Improvements for LTE).

SUMMARY OF THE INVENTION

Regarding movement of a radio terminal, a heterogeneous network has thefollowing problem.

When a radio terminal moving at a high speed switches a connected basestation (or a base station connected for stand-by) to a low-power basestation, the radio terminal has to immediately switch to another basestation because the cell of the low-power base station is small.

Accordingly, the problem is to consequently waste a resource consumed toswitch to the low-power base station and a resource consumed to switchfrom the low-power base station to another base station.

For this reason, an object of the present invention is to provide amobile communication method, a base station, a radio terminal, and alow-power base station, which can prevent unnecessary switching betweenbase stations in a heterogeneous network from consuming resources.

The present invention has the following features to solve the problemsdescribed above.

First of all, a mobile communication method according to a first featureof the present invention is summarized as follows. The mobilecommunication method comprises the steps of: notifying (S101 or S111),by abase station (macro base station MeNB) connected to a radio terminal(radio terminal UE) for communications or stand-by, the radio terminalof a plurality of parameters including a first parameter for high-speedmovement and a second parameter for non-high-speed movement asparameters for processing for switching to any of neighboring basestations; acquiring (S202 or S212), by the radio terminal, movementspeed information indicating a movement speed of the radio terminal; andselecting (S203 or S213), by the radio terminal, a parametercorresponding to the movement speed information from the plurality ofparameters notified by the base station, wherein the first parameter isconfigured to inhibit processing for switching to a low-power basestation (pico base station PeNB) which is included in the neighboringbase stations.

A base station according to a first feature of the present invention issummarized as follows. The base station (macro base station MeNB) to beconnected to a radio terminal (radio terminal UE) for communications orstand-by, comprises: a notification unit (radio communication unit 110and controller 140) configured to notify the radio terminal of aplurality of parameters including a first parameter for high-speedmovement and a second parameter for non-high-speed movement asparameters for processing for switching to any of neighboring basestations, wherein the first parameter is configured to inhibitprocessing for switching to a low-power base station (pico base stationPeNB) which is included in the neighboring base stations.

A radio terminal according to a first feature of the present inventionis summarized as follows. The radio terminal (radio terminal UE) in amobile communication system, comprises: a receiver (radio communicationunit 210) configured to receive a plurality of parameters including afirst parameter for high-speed movement and a second parameter fornon-high-speed movement as parameters for processing for switching to aneighboring base station from a base station (macro base station MeNB)connected to the radio terminal for communications or stand-by; anacquisition unit (controller 260) configured to acquire movement speedinformation indicating a movement speed of the radio terminal; and aselector (controller 260) configured to select a parameter correspondingto the movement speed information from the plurality of parametersreceived by the receiver, wherein the first parameter is configured toinhibit processing for switching to a low-power base station (pico basestation PeNB) which is included in the neighboring base stations.

A mobile communication method according to a second feature of thepresent invention is summarized as follows. The mobile communicationmethod comprises the steps of: notifying (S221 or S231), by a basestation (macro base station MeNB) connected to a radio terminal (radioterminal UE) for communications or stand-by, the radio terminal of aparameter for processing for switching to a neighboring base station;acquiring (S222 or S232), by the radio terminal, movement speedinformation indicating a movement speed of the radio terminal; andadjusting (S224 or S234), by the radio terminal, the parameter notifiedby the base station on the basis of the movement speed information,wherein the radio terminal adjusts the parameter notified by the basestation to inhibit processing for switching to a low-power base station(pico base station PeNB) which is included in the neighboring basestations when the movement speed information indicates high-speedmovement.

A radio terminal according to a second feature of the present inventionis summarized as follows. The radio terminal (radio terminal UE) in amobile communication system, comprising: a receiver (radio communicationunit 210) configured to receive a parameter for processing for switchingto any of neighboring base stations from a base station (macro basestation MeNB) connected to the radio terminal for communications orstand-by; an acquisition unit (controller 260) configured to acquiremovement speed information indicating a movement speed of the radioterminal; and an adjustment unit (controller 260) configured to adjustthe parameter received by the receiver on the basis of the movementspeed information, wherein the adjustment unit adjusts the parameterreceived by the receiver to inhibit processing for switching to alow-power base station (pico base station PeNB) which is included in theneighboring base station when the movement speed information indicateshigh-speed movement.

A mobile communication method according to a third feature of thepresent invention is summarized as follows. The mobile communicationmethod comprising the steps of: acquiring (S121), by a base station(macro base station MeNB) connected to a radio terminal (radio terminalUE), movement speed information indicating a movement speed of the radioterminal; selecting (S122), by the base station, a parametercorresponding to the movement speed information from a plurality ofparameters including a first parameter for high-speed movement and asecond parameter for non-high-speed movement as parameters forprocessing for handover to any of neighboring base stations; andnotifying (S123), by the base station, the radio terminal of theparameter selected in the selecting step, wherein the first parameter isconfigured to inhibit processing for handover to a low-power basestation (pico base station PeNB) which is included in the neighboringbase stations.

A base station according to a third feature of the present invention issummarized as follows. The base station (macro base station MeNB) to beconnected to a radio terminal (radio terminal UE), comprising: anacquisition unit (controller 140) configured to acquire movement speedinformation indicating a movement speed of the radio terminal; aselector (controller 140) configured to select a parameter correspondingto the movement speed information from a plurality of parametersincluding a first parameter for high-speed movement and a secondparameter for non-high-speed movement as parameters for processing forhandover to any of neighboring base stations; and a notification unit(radio communication unit 110 and controller 140) configured to notifythe radio terminal of the parameter selected by the selector, whereinthe first parameter is configured to inhibit processing for handover toa low-power base station (pico base station PeNB) which is included inthe neighboring base stations.

A mobile communication method according to a fourth feature of thepresent invention is summarized as follows. The mobile communicationmethod comprising the steps of: reporting (S401), from a radio terminal(radio terminal UE) to a base station connected to the radio terminal,measurement information on a measurement result of a received signalfrom at least one of the base station and each neighboring base station;acquiring (S404), by the base station, movement speed informationindicating a movement speed of the radio terminal; and transmitting(S406), from the base station to a low-power base station (pico basestation PeNB), a handover request for requesting an admission of theradio terminal when the measurement information reported from the radioterminal satisfies a handover condition to the low-power base stationwhich is included in the neighboring base stations, wherein the basestation halts (S407) transmission of the handover request to thelow-power base station when the measurement information reported fromthe radio terminal satisfies the handover condition to the low-powerbase station and the movement speed information indicates high-speedmovement.

In the mobile communication method according to a fourth feature of thepresent invention, the method further comprises the step of instructing(S408), by the base station, the radio terminal to halt processing for ameasurement of a received signal from the low-power base station whenthe movement speed information indicates high-speed movement.

A base station according to a fourth feature of the present invention issummarized as follows. The base station (macro base station MeNB) to beconnected to a radio terminal (radio terminal UE), comprising: areceiver (radio communication unit 110) configured to receivemeasurement information on a measurement result of a received signalfrom at least one of the base station and each neighboring base stationfrom the radio terminal; an acquisition unit (controller 140) configuredto acquire movement speed information indicating a movement speed of theradio terminal; and a transmitter (network communication unit 120 andcontroller 140) configured to transmit a handover request for requestingan admission of the radio terminal to a low-power base station (picobase station PeNB) when the measurement information received by thereceiver satisfies a handover condition to the low-power base station,wherein, when the measurement information reported from the radioterminal satisfies the handover condition for handover to the low-powerbase station and when the movement speed information indicateshigh-speed movement, the transmitter halts transmission of the handoverrequest to the low-power base station.

A mobile communication method according to a fifth feature of thepresent invention is summarized as follows. The mobile communicationmethod comprising the steps of: reporting (S411), from a radio terminal(radio terminal UE) to a base station (macro base station MeNB)connected to the radio terminal, measurement information on ameasurement result of a received signal from at least one of the basestation and each neighboring base station; acquiring (S413), by the basestation, movement speed information indicating a movement speed of theradio terminal; and transmitting (S417), from the base station to alow-power base station (pico base station PeNB) which is included in theneighboring base stations, a handover request for requesting anadmission of the radio terminal on the basis of the measurementinformation reported from the radio terminal, wherein the base stationtransmits (S415) the handover request including high-speed movementinformation when the movement speed information indicates high-speedmovement.

In the mobile communication method according to the fifth feature of thepresent invention, the method further comprises the steps of: receiving(S601) the handover request by the low-power base station: and rejecting(S603) the handover request by the low-power base station when thehandover request includes the high-speed movement information. Therejection of the handover request means transmitting negativeacknowledgement (NACK) in response to the handover request, or refers todisregarding and not responding to the handover request. This meaning issimilar in follows.

In the mobile communication method according to the fifth feature of thepresent invention, the method may further comprise the step ofinstructing (S416), by the base station, the radio terminal to haltprocessing for a measurement of a received signal from the low-powerbase station when the movement speed information indicates high-speedmovement.

A base station according to a fifth feature of the present invention issummarized as follows. The base station (macro base station MeNB) to beconnected to a radio terminal (radio terminal UE) comprises: a receiver(radio communication unit 110) configured to receive measurementinformation on a measurement result of a received signal from at leastone of the base station and each neighboring base station from the radioterminal; an acquisition unit (controller 140) configured to acquiremovement speed information indicating a movement speed of the radioterminal; and a transmitter (network communication unit 120 andcontroller 140) configured to transmit a handover request for requestingan admission of the radio terminal to a low-power base station (picobase station PeNB) which is included in the neighboring base stations onthe basis of the measurement information received by the receiver,wherein the transmitter transmits the handover request includinghigh-speed movement information when the movement speed informationindicates high-speed movement.

A low-power base station according to a fifth feature of the presentinvention is summarized as follows. The low-power base station (picobase station PeNB) comprises: a receiver (network communication unit320) configured to receive a handover request for requesting anadmission of a radio terminal (radio terminal UE) from a neighboringbase station; and a transmitter (network communication unit 320 andcontroller 340) configured to transmit a response to the handoverrequest to the neighboring base station, wherein the low-power basestation rejects the handover request when the handover request includeshigh-speed movement information indicating that the radio terminal ismoving at a high speed.

A mobile communication method according to a sixth feature of thepresent invention is summarized as follows. The mobile communicationmethod comprising the steps of: receiving (S611), by a low-power basestation (pico base station PeNB), a handover request for requesting anadmission of a radio terminal (radio terminal UE) from a neighboringbase station; requesting (S614), by the low-power base station, a corenetwork (EPC) for movement speed information indicating a movement speedof the radio terminal; acquiring (S615), by the low-power base station,the movement speed information from the core network; and transmitting(S617), from the low-power base station to the neighboring base station,a response to the handover request, wherein the low-power base stationrejects (S613) the handover request when the movement speed informationfrom the core network indicates high-speed movement.

A low-power base station according to a sixth feature of the presentinvention is summarized as follows. The low-power base station (picobase station PeNB) comprising: a receiver (network communication unit320) configured to receive a handover request for requesting anadmission of a radio terminal (radio terminal UE) from a neighboringbase station; an acquisition unit (network communication unit 320 andcontroller 340) configured to acquire movement speed information from acore network (EPC) after requesting the core network for the movementspeed information indicating a movement speed of the radio terminal; anda transmitter (network communication unit 320 and controller 340)configured to transmit a response to the handover request to theneighboring base station, wherein the low-power base station rejects thehandover request when the movement speed information from the corenetwork indicates high-speed movement.

A mobile communication method according to a seventh feature of thepresent invention is summarized as follows. The mobile communicationmethod comprises the steps of: measuring (S242), by a radio terminal(radio terminal UE), a received signal from at least one of a basestation (macro base station MeNB) connected to the radio terminal andeach neighboring base station: acquiring (S245), by the radio terminal,movement speed information indicating a movement speed of the radioterminal; and reporting (S244), from the radio terminal to the basestation, measurement information on a measurement result obtained in themeasuring step, wherein, when predetermined measurement information on ameasurement result of a received signal from a low-power base station(pico base station PeNB) is obtained by the measurement and when themovement speed information indicates high-speed movement, the radioterminal reports (S247) the measurement information from which thepredetermined measurement information is excluded.

A radio terminal according to a seventh feature of the present inventionis summarized as follows. The radio terminal (radio terminal UE) in amobile communication system, comprises: a measurement unit (radiocommunication unit 210 and controller 260) configured to measure areceived signal from at least one of a base station (macro base stationMeNB) connected to the radio terminal and each neighboring base station;an acquisition unit (controller 260) configured to acquire movementspeed information indicating a movement speed of the radio terminal; anda reporting unit (radio communication unit 210 and controller 260)configured to report measurement information on a measurement resultobtained by the measurement unit to the base station, wherein, whenpredetermined measurement information on a measurement result of areceived signal from a low-power base station (pico base station PeNB)is obtained by the measurement and when the movement speed informationindicates high-speed movement, the reporting unit reports themeasurement information from which the predetermined measurementinformation is excluded.

A mobile communication method according to an eighth feature of thepresent invention is summarized as follows. The mobile communicationmethod comprises the steps of: receiving (S421), by a base station(macro base station MeNB) connected to a radio terminal (radio terminalUE), measurement information on a measurement result of a receivedsignal from at least one of the base station and each neighboring basestation from the radio terminal; acquiring (S423), by the base station,movement speed information indicating a movement speed of the radioterminal; and determining (S426), by the base station, a handover targetof the radio terminal on the basis of the measurement informationreceived from the radio terminal, wherein, when predeterminedmeasurement information on a measurement result of a received signalfrom a low-power base station (pico base station PeNB) is included inthe measurement information and when the movement speed informationindicates high-speed movement, the base station decides the handovertarget of the radio terminal after excluding (S425) the predeterminedmeasurement information which is included in the measurementinformation.

A base station according to an eighth feature of the present inventionis summarized as follows. The base station (macro base station MeNB) tobe connected to a radio terminal (radio terminal UE), comprises: areceiver (radio communication unit 110) configured to receivemeasurement information on a measurement result of a received signalfrom at least one of the base station and each neighboring base stationfrom the radio terminal; an acquisition unit (controller 140) configuredto acquire movement speed information indicating a movement speed of theradio terminal; and a decision unit (controller 140) configured todecide a handover target of the radio terminal on the basis of themeasurement information received by the receiver, wherein, whenpredetermined information on a measurement result of a received signalfrom a low-power base station (pico base station PeNB) is included inthe measurement information and when the movement speed informationindicates high-speed movement, the decision unit decides the handovertarget of the radio terminal after excluding the predeterminedmeasurement information which is included in the measurementinformation.

The present invention can provide a mobile communication method, a basestation, a radio terminal, and a low power base station which canprevent unnecessary switching between base stations in a heterogeneousnetwork from consuming resources.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing for describing a network configuration of a mobilecommunication system according to first to eighth embodiments.

FIG. 2 is a block diagram of a macro base station according to the firstto eighth embodiments.

FIG. 3 is a block diagram of a radio terminal according to the first toeighth embodiments.

FIG. 4 is a block diagram of a pico base station according to the firstto eighth embodiments.

FIG. 5 is a drawing for describing an operation environment of themobile communication system according to the first to eighthembodiments.

FIG. 6 is an operational sequence diagram of handover procedures fromthe macro base station to the pico base station;

FIG. 7 is a flowchart of measurement configuration transmissionprocessing according to the first embodiment;

FIG. 8 is a flowchart of measurement processing according to the firstembodiment.

FIG. 9 is a flowchart of measurement processing according to the secondembodiment.

FIG. 10 is a flowchart of measurement configuration transmissionprocessing according to the third embodiment;

FIG. 11 is a flowchart of handover decision processing according to thefourth embodiment.

FIG. 12 is a flowchart of handover decision processing and handoverrequest transmission processing according to the fifth embodiment.

FIG. 13 is a flowchart of admission decision processing according to thefifth embodiment.

FIG. 14 is a flowchart of admission decision processing according to thesixth embodiment.

FIG. 15 is a flowchart of measurement processing according to theseventh embodiment.

FIG. 16 is a flowchart of handover decision processing according to theeighth embodiment;

FIG. 17 is an operational sequence diagram of cell reselectionprocedures from the macro base station to the pico base station.

FIG. 18 is an operational flowchart of the macro base station when thefirst embodiment is applied to the cell reselection.

FIG. 19 is an operational flowchart of the radio terminal when the firstembodiment is applied to the cell reselection.

FIG. 20 is an operational flowchart of the radio terminal when thesecond embodiment is applied to the cell reselection.

DESCRIPTION OF THE EMBODIMENTS

Referring to the drawings, first to eighth embodiments and otherembodiments of the present invention are described. In the drawings ineach embodiment, same or similar reference numerals are given to denotesame or similar portions.

Summary of Embodiments

A mobile communication system according to the first to eighthembodiments is configured based on LTE whose specifications are designedby the 3GPP. Also, a heterogeneous network is introduced into the mobilecommunication system. As described above, the heterogeneous networkincludes not only a high-power base station (so-called, a macro basestation) but also a low-power base station with a small cell, which areeffectively deployed in the network (for example, located in ahigh-traffic area). In the first to eighth embodiments, a pico basestation which is one type of a low-power base station is described as anexample.

FIG. 1 is a drawing for illustrating a network configuration of themobile communication system.

As shown in FIG. 1, the mobile communication system includes a radioterminal UE, a macro base station MeNB, a pico cell base station PeNB, amacro base station MeNB′, a mobility management device MME, and agateway device S-GW. In the following description, when the macro basestation MeNB and the Pico base station PeNB are not particularlydistinguished from each other, they are simply referred to as a “basestation eNB”.

The radio terminal UE is a radio communication device which is held by auser and moves along with the movement of the user. The radio terminalUE connects with any of multiple base stations eNB to performcommunications via the connected base station eNB. A state where theradio terminal UE is communicating is referred to as a connected state(or a connected mode), while a state where the radio terminal UE is instandby without executing a communication is referred to as an idlestate (or an idle mode).

The plurality of base stations eNB forms E-UTRAN (Evolved-UMTSTerrestrial Radio Access Network) which is a radio access network. Eachof the plurality of base stations eNB forms a cell in which the radioterminal UE is provided with a service. The cell which is formed by eachbase station eNB forms a wide-range service area. Each of the pluralityof base stations eNB constantly broadcasts a reference signal (RS) withwhich the base station can be identified. Such a reference signal issometimes referred to as a pilot signal.

The radio terminal UE switches to a base station eNB with a morepreferable radio condition as it moves. Such base station switching isreferred to as handover in the connected state and as a cell reselectionin the idle state. In the mobile communication system, a base stationeNB connected to the radio terminal UE has rights to decide whether tohandover the radio terminal UE and to decide a handover target.

The neighboring base stations eNB can perform base stationcommunications using an X2 interface which is a logical interface. Eachbase station eNB transmits/receives a control signal which is used forhandover control or the like, using the X2 interface.

The mobility management device MME and the gateway device S-GW form EPC(Evolved Packet Core) which is a core network. Each base station eNBcommunicates with the mobility management device MME and the gatewaydevice S-GW which are included in EPC, using an S1 interface which is alogical interface for communication with EPC. The mobility managementdevice MME executes a control plane function for enabling mainly userauthentication, paging, interconnection with other systems, and the likeand transmits/receives a control signal to/from each base station eNB.On the other hand, the gateway device S-GW executes a user planefunction for transferring user data and transmits/receives a data packetto/from each base station eNB.

Hereinafter, referring to FIGS. 2 to 4, respective configurations of themacro base station MeNB, the radio terminal UE, and the pico basestation PeNB are described.

FIG. 2 is a functional block configuration diagram of the macro basestation MeNB. As shown in FIG. 2, the macro base station MeNB includesan antenna 101, a radio communication unit 110, a network communicationunit 120, a storage unit 130, and a controller 140.

The antenna 101 is used for transmission and reception of a radiosignal. The radio communication unit 110 is configured to perform aradio communication through the antenna 101. As for transmission, theradio communication unit 110 performs up-convert and amplification of abaseband signal which is inputted from the controller 140 and outputs aradio signal through the antenna 101. As for reception, the radiocommunication unit 110 performs amplification and down-convert of areceived signal which is inputted from the antenna 101 and, thereafter,outputs a baseband signal to the controller 140.

The network communication unit 120 communicates with the core networkEPC and neighboring base stations. Specifically, the networkcommunication unit 120 communicates with the gateway device S-GW and themobility management device MME which are included in the core networkEPC, using the S1 interface. Also, the network communication unit 120communicates with the pico base station PeNB and the macro base stationMeNB′, using the X2 interface.

The storage unit 130 is configured using, for example, a memory, andstores various pieces of information to be used for control which isperformed by the controller 140 and the like. The controller 140 isconfigured using, for example, a CPU and controls various kinds offunctions included in the macro base station MeNB.

FIG. 3 is a block configuration diagram of the radio terminal UE. Asshown in FIG. 3, the radio terminal UE includes an antenna 201, a radiocommunication unit 210, a user interface unit 220, a GPS receiver 230, abattery 240, a storage unit 250, and a controller 260. However, theradio terminal UE does not necessarily includes the GPS receiver 230.Also, the radio terminal UE configured as, for example, a card-typeterminal, does not include the user interface unit 220 and the battery240.

The antenna 201 is used for transmission and reception of a radiosignal. The radio communication unit 210 is configured so as to performa radio communication through the antenna 201. As for transmission, theradio communication unit 210 performs up-convert and amplification of abaseband signal which is inputted from the controller 260 and outputs aradio signal through the antenna 201. As for reception, the radiocommunication unit 210 performs amplification and down-convert of areceived signal which is inputted through the antenna 201 and,thereafter, outputs a baseband signal to the controller 260.

The user interface unit 220 includes a button to accept an operationfrom a user and a display to display an image, and functions as aninterface with the user of the radio terminal UE. The GPS receiver 230receives a GPS signal and outputs location information indicating acurrent location of the radio terminal UE to the controller 260. Thebattery 240 stores power which is supplied to each block of the radioterminal UE. The storage unit 250 is configured using, for example, amemory, and stores various pieces of information to be used for controlperformed by the controller 260 and the like. The controller 260 isconfigured using, for example, a CPU and controls various kinds offunctions included in the radio terminal UE.

FIG. 4 is a block configuration diagram of the pico base station PeNB.As shown in FIG. 4, the pico base station PeNB includes an antenna 301,a network communication unit 320, a storage unit 330, and a controller340.

The antenna 301 is used for transmission and reception of a radiosignal. The radio communication unit 310 is configured so as to performa radio communication through the antenna 301. As for transmission, theradio communication unit 310 performs up-convert and amplification of abaseband signal which is inputted from the controller 340 and outputs aradio signal through the antenna 301. As for reception, the radiocommunication unit 310 performs amplification and down-convert of areceived signal which is inputted through the antenna 301 and,thereafter, outputs a baseband signal to the controller 340.

The network communication unit 320 communicates with the core networkEPC and neighboring base stations. Specifically, the networkcommunication unit 320 communicates with the gateway device S-GW and themobility management device MME which are included in the core networkEPC, using the S1 interface. Also, the network communication unit 320communicates with the macro base station MeNB and the macro base stationMeNB′, using the X2 interface.

The storage unit 330 is configured using, for example, a memory, andstores various pieces of information to be used for control performed bythe controller 340 and the like. The controller 340 is configured using,for example, a CPU and controls various kinds of functions included inthe pico base station PeNB.

Hereinafter, an operation environment of the mobile communication systemis described. FIG. 5 is a drawing for describing an operationenvironment of the mobile communication system.

As shown in FIG. 5, in the mobile communication system, the pico basestation PeNB is located in the neighborhood of the macro base stationMeNB within a cell which is formed by the macro base station MeNB. TheMacro base station MeNB′ is located in the neighborhood of the macrobase station MeNB outside the cell which is formed by the macro basestation MeNB. In other words, the pico base station PeNB and the macrobase station MeNB′ correspond to neighboring base stations in theneighborhood of the macro base station MeNB.

The radio terminal UE is located within the cell of the macro basestation MeNB and is connected to and communicates with the macro basestation MeNB. Also, the radio terminal UE is moving toward a cell of thepico base station PeNB.

Here, the description is given on an outline of handover procedures inthe handover from the macro base station MeNB to the pico base stationPeNB in the mobile communication system. FIG. 6 is an operationalsequence diagram of the handover procedures from the macro base stationMeNB to the pico base station PeNB.

As shown in FIG. 6, at step S1, the macro base station MeNB transmits ameasurement configuration for configuring measurement and reporting of ameasurement result, which should be performed by the radio terminal UE,to the radio terminal UE. The measurement means, for example,measurement of reference signal received power (RSRP) or a referencesignal received quality (RSRQ). The measurement configuration includes aparameter for controlling the measurement and reporting of themeasurement result which should be performed by the radio terminal UE.

The parameter includes a measurement target and a reporting condition.The measurement target is designated with a measurement ID for each basestation (a cell), for example. The reporting condition includesinformation designating a periodic report or an event-triggered report,or information indicating a designated event (in other words, areporting condition) in the case of the event-triggered report.

The reporting condition includes a condition that a measurement value(RSRP/RSRQ) of a neighboring base station (a neighboring cell) becomeshigher than a value obtained by adding an offset to the measurementvalue of the macro base station MeNB (the serving cell), a conditionthat RSRP/RSRQ of the macro base station MeNB becomes lower than athreshold, and a condition that a RSRP/RSRQ of the neighboring basestation exceeds a threshold. Note that in the event-triggered report, anoverhead can be reduced as compared with the periodic report.

At step S2, the radio terminal UE decides whether to report themeasurement result after the measurement is conducted according to theparameter included in the measurement configuration. In the case of theperiodic report, the decision is conducted depending on whether a timerhas expired, while in the case of the event-triggered report, thedecision is conducted depending on whether a timer has expired after thereporting condition is satisfied.

At step S3, the radio terminal UE transmits a measurement ID of a basestation (a cell) which is a target for measurement and a measurementreport including the measurement information which is configured inassociation with the measurement result to the macro base station MeNB.Specifically, in the case of the periodic report, the measurementinformation for each measurement ID is included in the measurementreport, while in the case of the event-triggered report, only themeasurement information for the measurement ID corresponding to thereporting condition is included in the measurement report.

At step S4, the macro base station MeNB decides whether to perform ahandover on the basis of the measurement report received from the radioterminal UE. When it is decided to perform the handover, the macro basestation MeNB decides a handover target. It is assumed here that thehandover to the pico base station PeNB is decided to be performed.

At step S5, the macro base station MeNB transmits a handover request forrequesting admission of the radio terminal UE to the pico base stationPeNB, using the X2 interface.

At step S6, the pico base station PeNB decides whether to permit theadmission of the radio terminal UE on the basis of the handover requestreceived from the macro base station MeNB. For example, the admissioncan be decided to be rejected when the pico base station PeNB is in ahigh-load state. It is assumed here that the admission of the radioterminal UE is permitted.

At step S7, the pico base station PeNB transmits a handover request Ackwhich is an affirmative response to the handover request to the macrobase station MeNB, using the X2 interface.

At step S8, the macro base station MeNB transmits a handover command forinstructing the handover in response to the reception of the handoverrequest Ack from the pico base station eNB, to the radio terminal.

At step S9, the radio terminal UE disconnects from the macro basestation MeNB in response to the reception of the handover command fromthe macro base station MeNB and establishes the connection (establishessynchronization) with the pico base station PeNB.

At step S10, the radio terminal UE transmits a Conn.Reconfig. Completefor notifying that switching of the connected base station has beencompleted to the pico base station PeNB.

The handover from the macro base station MeNB to the pico base stationPeNB is performed with these procedures. However, there are a number ofcommunications (signaling) of the control signal along with thehandover. Thus, a large amount of resources is consumed.

As shown in FIG. 5, the radio terminal UE which moves to a vicinity ofthe pico base station PeNB can execute handover to the pico base stationPeNB with the above-described handover procedures.

However, when the radio terminal UE is moving at a high speed becausethe radio terminal UE is on a vehicle, for example, there is a need toperform handover from the pico base station PeNB to the macro basestation MeNB′ just after the handover to the pico base station PeNB isperformed. Accordingly, the resource which is consumed for the handoverto the pico base station PeNB and the resource which is consumed for thehandover from the pico base station PeNB to the macro base station MeNB′are wasted as a result.

For this reason, the first to eighth embodiments to be described belowsolve a problem of a heterogeneous network which is caused by ahigh-speed movement of the radio terminal UE by improving theabove-described handover procedures.

First Embodiment

In the first embodiment, the measurement configuration transmissionprocessing (step S1 in FIG. 6) and the measurement processing (step S2in FIG. 6) in the above-described handover procedures are improved.

Referring back to FIGS. 2 and 3, an operation of each of the macro basestation MeNB and the radio terminal UE according to the first embodimentis described.

As shown in FIG. 2, the storage unit 130 of the macro base station MeNBaccording to the first embodiment stores in advance multiple parameters(parameters for each movement speed) including a first parameter forhigh-speed movement and a second parameter for non-high-speed movementas parameters to be included in a measurement configuration.

The first parameter for high-speed movement is configured to inhibit ameasurement report which triggers handover to the pico base stationPeNB. On the other hand, the second parameter for non-high-speedmovement is configured to allow the measurement Report which triggersthe handover to the pico base station PeNB.

For example, the first parameter for high-speed movement is configuredas follows.

-   -   The first parameter has the pico base station PeNB excluded from        a measurement target.    -   In the case of the event-triggered report, when the condition        that RSRP/PSRQ of the pico base station PeNB exceeds a threshold        is used as a reporting condition, the threshold of the first        parameter is set to be significantly higher than a threshold of        the second parameter.    -   In the case of the event-triggered report, when the condition        that a value obtained by adding an offset to RSRP/RSRQ of the        macro base station MeNB becomes lower than RSRP/RSRQ of the pico        base station PeNB is used as a reporting condition, the first        parameter is set as an offset value by which the RSRP/RSRQ of        the macro base station MeNB is increased.

Also, the controller 140 of the macro base station MeNB controls theradio communication unit 110 so that the parameters for respectivemovement speeds which are stored in the storage unit 130 are read, and,thereafter, transmit the measurement configuration including the readparameters for respective movement speeds. As described above, in thefirst embodiment, the radio communication unit 110 and the controller140 correspond to notification units configured to notify the radioterminal UE of the plurality of parameters including the first parameterfor high-speed movement and the second parameter for non-high-speedmovement.

As shown in FIG. 3, the radio communication unit 210 of the radioterminal UE according to the first embodiment receives the measurementconfiguration including the parameters for respective movement speeds.In other words, in the first embodiment, the radio communication unit210 corresponds to a receiver configured to receive the plurality ofparameters including the first parameter for high-speed movement and thesecond parameter for non-high-speed movement.

Also, the controller 260 of the radio terminal UE corresponds to anacquisition unit configured to acquire movement speed informationindicating a movement speed of the radio terminal UE. For example, thecontroller 260 acquires movement speed information as follows.

-   -   The controller 260 measures a fading frequency of a radio signal        which is received by the radio communication unit 210.

Since a higher fading frequency means that the radio terminal UE ismoving at a higher speed, a movement speed which is estimated by thefading frequency or a distribution of the fading frequency is used asmovement speed information.

-   -   The controller 260 measures the number of handovers/the number        of cell reselections per unit time. Since the larger number of        handovers/the higher number of cell reselections per unit time        means that the radio terminal UE is moving at a higher speed, a        movement speed which is estimated by the number of handovers/the        number of cell reselections per unit time is used as movement        speed information.    -   The controller 260 measures a travelling distance per unit time        using a GPS receiver 230 when the radio terminal UE has the GPS        receiver 230. Accordingly, a movement speed is obtained from the        travelling distance per unit time, and thus the obtained        movement speed is used as movement speed information.    -   The controller 260 acquires the movement speed information by        inquiring a network (the radio access network E-UTRAN or the        core network EPC) about the movement speed of the radio terminal        UE.

Also, the controller 260 corresponds to a selector configured to selecta parameter corresponding to the acquired movement speed informationfrom the parameters for respective movement speeds which are received bythe radio communication unit 210. For example, the controller 260selects the first parameter for high-speed movement when the movementspeed information indicates high-speed movement. The controller 260performs the above-described measurement processing using the selectedparameter.

Next, referring to FIGS. 7 and 8, the measurement configurationtransmission processing and the measurement processing according to thefirst embodiment are described.

FIG. 7 is a flowchart of the measurement configuration transmissionprocessing according to the first embodiment.

As shown in FIG. 7, at step S101, the macro base station MeNB transmitsthe measurement configuration including the plurality of parameters(parameters for respective movement speeds) including the firstparameter for high-speed movement and the second parameter fornon-high-speed parameter.

FIG. 8 is a flowchart of the measurement processing according to thefirst embodiment.

As shown in FIG. 8, at step S201, the radio terminal UE receives themeasurement configuration including the parameters for respectivemovement speeds.

At step S202, the radio terminal UE acquires the movement speedinformation indicating the movement speed of the radio terminal UE.

At step S203, the radio terminal UE selects a parameter corresponding tothe movement speed information acquired at step S202 from the parametersfor respective movement speeds received at step S201.

At step S204, the radio terminal UE measures RSRP/RSRQ of a measurementtarget base station (a measurement target cell) which is designated bythe parameter selected at step S203.

At step S205, the radio terminal UE decides whether the measurementresult obtained at step S204 satisfies the reporting condition which isdesignated by the parameter selected at step S203.

When it is decided that the reporting condition is satisfied (step S205;YES), at step S206, the radio terminal UE transmits a measurement reportrelating to the measurement result obtained at step S204 to the macrobase station MeNB.

As described above, according to the first embodiment, the micro basestation MeNB transmits the measurement configuration including theparameters for respective movement speeds, and the radio terminal UEselects and uses the parameter corresponding to the movement speed ofthe radio terminal UE from the parameters for respective movementspeeds, so that the handover to the pico base station PeNB can beavoided and unnecessary handover in the heterogeneous network can beprevented.

Second Embodiment

In the second embodiment, the measurement processing (step S2 in FIG. 6)in the above-described handover procedures is improved.

Referring to FIG. 3, an operation of a radio terminal UE according tothe second embodiment is described.

As shown in FIG. 3, a radio communication unit 210 of the radio terminalUE according to the second embodiment receives a measurementconfiguration including parameters from a macro base station MeNB. Inother words, in the second embodiment, the radio communication unit 210corresponds to a receiver configured to receive the parameters.

Also, a controller 260 of the radio terminal UE corresponds to anacquisition unit configured to acquire movement speed information. Amethod of acquiring the movement speed information is similar to that ofthe first embodiment.

Furthermore, the controller 260 corresponds to an adjustment unitconfigured to adjust the parameter which is received by the radiocommunication unit 210. Specifically, the controller 260 adjusts theparameter which is received by the radio communication unit 210 so thata measurement report which triggers handover to a pico base station PeNBis inhibited when the acquired movement speed information indicateshigh-speed movement.

For example, the controller 260 adjusts the parameter as follows whenthe acquired movement speed information indicates high-speed movement.

-   -   The parameter is set such that a pico base station PeNB is        excluded from a measurement target.    -   In the case of an the event-triggered report, when the condition        that RSRP/PSRQ of the pico base station PeNB exceeds a threshold        is used as the reporting condition, a threshold as the parameter        is set to be significantly high.    -   In the case of the event-triggered report, when the condition        that a value obtained by adding an offset to RSRP/RSRQ of the        macro base station MeNB becomes lower than RSRP/RSRQ of the pico        base station PeNB is used as the reporting condition, offset        processing is performed to relatively increase the RSRP/RSRQ of        the macro base station MeNB.

With these adjustments, the measurement report which triggers thehandover to the pico base station PeNB is inhibited. After that, thecontroller 260 performs the above-described measurement processing usingthe adjusted parameter.

Next, referring to FIG. 9, measurement processing according to thesecond embodiment is described. FIG. 9 is a flowchart of the measurementprocessing according to the second embodiment.

As shown in FIG. 9, at step S221, the radio terminal UE receives themeasurement configuration including the parameter.

At step S222, the radio terminal UE acquires movement speed informationindicating a movement speed of the radio terminal UE.

At step S223, the radio terminal UE decides whether the movement speedinformation acquired at step S222 indicates high-speed movement.

When it is decided that the movement speed information acquired at stepS222 indicates high-speed movement (step S223; YES), at step S224, theradio terminal UE adjusts the parameter received at step S221 so thatthe measurement report which triggers the handover to the pico basestation PeNB is inhibited. On the other hand, when it is decided thatthe movement speed information acquired at step S222 does not indicatehigh-speed movement (step S223; NO), the radio terminal UE proceeds tostep S225.

At step S225, the radio terminal UE measures RSRP/RSRQ of a measurementtarget base station (a measurement target cell) which is designated bythe parameter.

At step S226, the radio terminal UE decides whether the measurementresult obtained at step S225 satisfies a reporting condition which isdesignated by the parameter.

When it is decided that the reporting condition is satisfied (step S226;YES), at step S227, the radio terminal UE transmits the measurementreport relating to the measurement result obtained at step S225 to themacro base station MeNB.

As described above, according to the second embodiment, the radioterminal UE adjusts the parameter included in the received measurementconfiguration when the movement speed of the radio terminal UE is a highspeed, so that the handover to the pico base station PeNB can be avoidedand unnecessary handover in the heterogeneous network can be prevented.

Third Embodiment

In the third embodiment, the measurement configuration transmissionprocessing (step S1 in FIG. 6) in the above-described handoverprocedures is improved.

Referring back to FIG. 2, an operation of a macro base station MeNBaccording to the third embodiment is described.

As shown in FIG. 2, a storage unit 130 of the macro base station MeNBaccording to the third embodiment stores in advance multiple parameters(parameters for respective movement speeds) including the firstparameter for high-speed movement and the second parameter fornon-high-speed movement as parameters to be included in a measurementconfiguration.

The first parameter for high-speed movement is configured to inhibit ameasurement report which triggers handover to a pico base station PeNB.On the other hand, the second parameter for non-high-speed movement isconfigured to allow the measurement report which triggers the handoverto the pico base station PeNB.

For example, the first parameter for high-speed movement is configuredas follows.

-   -   In the first parameter, a pico base station PeNB is excluded        from a measurement target.    -   In the case of the event-triggered report, when the condition        that RSRP/PSRQ of the pico base station PeNB exceeds a threshold        is used as the reporting condition, a threshold as the first        parameter is set to be significantly higher than a threshold as        the second parameter.    -   In the case of the event-triggered report, when the condition        that a value obtained by adding an offset to RSRP/RSRQ of the        macro base station MeNB becomes lower than RSRP/RSRQ of the pico        base station PeNB is used as the reporting condition, the first        parameter is set as an offset value by which the RSRP/RSRQ of        the macro base station MeNB is increased.

Also, a controller 140 of the macro base station MeNB corresponds to anacquisition unit configured to acquire movement speed informationindicating a movement speed of the radio terminal UE. For example, thecontroller 140 acquires movement speed information as follows.

-   -   The controller 140 measures a fading frequency of a radio signal        which is received by the radio communication unit 110 from the        radio terminal UE. Since a higher fading frequency means that        the radio terminal UE is moving at a higher speed, a movement        speed which is estimated by the fading frequency or a        distribution of the fading frequency is used as movement speed        information.    -   The controller 140 demands the movement speed information from        the radio terminal UE when the radio terminal UE can acquire the        movement speed information, so that the movement speed        information from the radio terminal UE is acquired.    -   The controller 140 acquires the movement speed information from        the core network EPC by inquiring the core network EPC about the        movement speed of the radio terminal UE.

Also, the controller 140 corresponds to a selector configured to selecta parameter corresponding to the acquired movement speed informationfrom the parameters for respective movement speeds which are stored inthe storage unit 130. For example, the controller 140 selects the firstparameter for high-speed movement when the movement speed informationindicates high-speed movement.

After that, the controller 140 reads the selected parameter from thestorage unit 130, and, thereafter, controls the radio communication unit110 so that the measurement configuration including the parameter istransmitted. As described above, in the third embodiment, the radiocommunication unit 110 and the controller 140 correspond to notificationunits configured to notify the radio terminal UE of the selectedparameter.

Next, referring to FIG. 10, measurement configuration transmissionprocessing according to the third embodiment is described. FIG. 10 is aflowchart of the measurement configuration transmission processingaccording to the third embodiment.

As shown in FIG. 10, at step S121, the macro base station MeNB acquiresmovement speed information indicating a movement speed of the radioterminal UE.

At step S122, the macro base station MeNB selects a parametercorresponding to the movement speed information acquired at step S121from the parameters for respective movement speeds.

At step S123, the macro base station MeNB transmits the measurementconfiguration including the parameter selected at step S122 to the radioterminal UE.

As described above, according to the third embodiment, the micro basestation MeNB selects a parameter which corresponds to the movement speedof the radio terminal UE from the parameters for respective movementspeeds and includes the parameter in the measurement configuration, sothat the handover to the pico base station PeNB can be avoided andunnecessary handover in the heterogeneous network can be prevented.

Fourth Embodiment

In the fourth embodiment, the handover decision processing (step S4 inFIG. 6) in the above-described handover procedures is improved.

Referring back to FIG. 2, an operation of a macro base station MeNBaccording to the fourth embodiment is described.

As shown in FIG. 2, a radio communication unit 110 of the macro basestation MeNB according to the fourth embodiment corresponds to areceiver configured to receive a measurement report from a radioterminal UE.

Also, a controller 140 of the macro base station MeNB corresponds to anacquisition unit configured to acquire movement speed informationindicating a movement speed of the radio terminal UE. A method ofacquiring the movement speed information is similar to that of the thirdembodiment.

Also, the controller 140 decides whether the measurement report which isreceived by the radio communication unit 110 satisfies a condition forhandover to a pico base station PeNB. For example, it is decided that ameasurement ID corresponding to the pico base station PeNB is includedin the measurement report and a measurement result corresponding to themeasurement ID satisfies the handover condition.

Then, when it is decided that the condition for handover to the picobase station PeNB is satisfied, the controller 140 controls the networkcommunication unit 120 so that the handover request for requesting anadmission of a radio terminal UE is transmitted to the pico base stationPeNB. In this manner, in the fourth embodiment, the networkcommunication unit 120 and the controller 140 correspond to transmittersconfigured to transmit the handover request.

However, in a case where the condition for handover to the pico basestation PeNB is satisfied but the acquired movement speed informationindicates high-speed movement, the controller 140 performs control sothat the transmission of the handover request to the pico base stationPeNB is halted.

Next, referring to FIG. 11, handover decision processing according tothe fourth embodiment is described. FIG. 11 is a flowchart of thehandover decision processing according to the fourth embodiment.

As shown in FIG. 11, at step S401, the macro base station MeNB receivesthe measurement report from the radio terminal UE.

At step S402, the macro base station MeNB decides whether themeasurement request received at step S401 satisfies the condition forhandover to the pico base station PeNB.

When it is decided that the measurement report does not satisfy thecondition for handover to the pico base station PeNB (step S402; NO), atstep S403, the macro base station MeNB performs normal handover decisionprocessing, that is, processing similar to the above-described handoverprocedures.

On the other hand, when it is decided that the measurement reportsatisfies the condition for handover to the pico base station PeNB (stepS402; YES), at step S404, the macro base station MeNB acquires movementspeed information indicating a movement speed of the radio terminal UE.

At step S405, the macro base station MeNB decides whether the movementspeed information acquired at step S404 indicates high-speed movement.

When it is decided that the movement speed information acquired at stepS404 does not indicate high-speed movement (step S405; NO), at stepS406, the macro base station MeNB transmits the handover request to thepico base station PeNB.

On the other hand, when it is decided that the movement speedinformation acquired at step S404 indicates high-speed movement (stepS405; YES), at step S407, the macro base station MeNB halts thetransmission of the Handover request to the pico base station PeNB.

Furthermore, at step S408, the macro base station MeNB instructs theradio terminal UE to halt the processing for the measurement on the picobase station PeNB. Specifically, an instruction is given through themeasurement configuration so that measurement on the pico base stationPeNB is not performed or that a measurement result of the pico basestation PeNB is not reported.

As described above, according to the fourth embodiment, in the casewhere the condition for handover to the pico base station PeNB issatisfied but the movement speed of the radio terminal UE is a highspeed, the macro base station halts the transmission of the handoverrequest to the pico base station PeNB, so that the handover to the picobase station PeNB can be avoided and unnecessary handover in theheterogeneous network can be prevented.

Also, according to the fourth embodiment, the transmission of thehandover request is halted and then the radio terminal UE is instructedto halt the processing for the measurement on the pico base stationPeNB. This can prevent a similar measurement report from beingrepeatedly generated and can decrease the overhead.

Fifth Embodiment

The fifth embodiment is such that the handover decision processing (stepS4 in FIG. 6), the handover request transmission processing (S5 in FIG.6), and the admission decision processing (step S6 in FIG. 6) in theabove-described handover procedures are improved.

Referring back to FIGS. 2 and 4, an operation of each of a macro basestation MeNB and a pico base station PeNB according to the fifthembodiment is described.

As shown in FIG. 2, a radio communication unit 110 of the macro basestation MeNB according to the fifth embodiment corresponds to a receiverconfigured to receive a measurement report from a radio terminal UE.

Also, a controller 140 of the macro base station MeNB corresponds to anacquisition unit configured to acquire movement speed informationindicating a movement speed of the radio terminal UE. A method ofacquiring the movement speed information is similar to that of the thirdembodiment.

Also, the controller 140 decides whether the measurement report which isreceived by the radio communication unit 110 satisfies a condition forhandover to a neighboring base station. Then, when it is decided thatthe condition for handover to the neighboring base station is satisfied,the controller 140 controls the network communication unit 120 so thatthe handover request for requesting an admission of the radio terminalUE is transmitted to the neighboring base station. In this manner, inthe fourth embodiment, the network communication unit 120 and thecontroller 140 correspond to transmitters configured to transmit thehandover request.

However, the controller 140 performs control so that the handoverrequest including the high-speed movement information is transmittedwhen the acquired movement speed information indicates high-speedmovement. The high-speed movement information is, for example, 1-bitinformation (flag) in which “1” indicates high-speed movement and “0”indicates movement slower than the high-speed movement. Note that theinformation is not limited to the 1-bit information but may bemultiple-bits information so that movement speed can be expressed morein detail.

Note that, in the fifth embodiment, the macro base station MeNB does notneed to know whether a base station as a transmission destination of thehandover request is a pico base station.

As shown in FIG. 4, the network communication unit 320 of the pico basestation PeNB according to the fifth embodiment corresponds to a receiverconfigured to receive a measurement request.

A controller 340 of the pico base station PeNB decides whether thehandover request which is received by the network communication unit 320includes high-speed movement information. The controller 340 controlsthe network communication unit 320 so that the handover request Ack istransmitted to a transmission source of the handover request when thehigh-speed movement information is not included in the handover requestand another admission condition is satisfied.

However, in a case where another admission condition is satisfied butthe high-speed movement information is included in the handover request,the controller 340 performs control of terminating the transmission ofthe handover request Ack and of not responding to the handover requestor transmitting a handover request Nack.

In this manner, in the fifth embodiment, the network communication unit320 and the controller 340 correspond to transmitters configured totransmit the handover request Ack or handover request Nack.

Note that when a macro base station MeNB′ receives a handover requestincluding high-speed movement information, the macro base station MeNB′performs admission decision processing by ignoring the high-speedmovement information.

Next, referring to FIG. 12, handover decision processing and handoverrequest transmission processing according to the fifth embodiment aredescribed. FIG. 12 is a flowchart of handover decision processing andhandover request transmission processing according to the fifthembodiment.

As shown in FIG. 12, at step S411, the macro base station MeNB receivesthe measurement report from the radio terminal UE.

At step S412, the macro base station MeNB decides whether themeasurement report received at step S411 satisfies a condition forhandover to a neighboring base station.

When it is decided that the measurement report satisfies the conditionfor handover to a pico base station PeNB (step S412; YES), at step S413,the macro base station MeNB acquires movement speed informationindicating a movement speed of the radio terminal UE.

At step S414, the macro base station MeNB decides whether the movementspeed information acquired at step S404 indicates high-speed movement.

When it is decided that the movement speed information acquired at stepS413 does not indicate high-speed movement (step S414; NO), at stepS417, the macro base station MeNB transmits a normal handover request tothe pico base station PeNB.

On the other hand, when it is decided that the movement speedinformation acquired at step S413 indicates high-speed movement (stepS414; YES), at step S415, the macro base station MeNB transmits thehandover request including the high-speed movement information to theneighboring base station.

Note that when the type of the base station as the transmissiondestination of the handover request has been identified as the pico basestation, the macro base station MeNB may transmit the handover requestincluding the high-speed movement information to the pico base stationPeNB, and thereafter, at step S416, may instruct the radio terminal UEto halt the processing for the measurement on the pico base stationPeNB. Specifically, instruction is given through the measurementconfiguration so that measurement on the pico base station PeNB is notperformed, or that a measurement result of the pico base station PeNB isnot reported.

Next, referring to FIG. 13, admission decision processing according tothe fifth embodiment is described. FIG. 13 is a flowchart of admissiondecision processing according to the fifth embodiment.

As shown in FIG. 13, at step S601, the pico base station MeNB receives ahandover request from the macro base station MeNB.

At step S602, the pico base station PeNB decides whether the handoverrequest received at step S601 satisfies an admission condition.

When it is decided that the admission condition is not satisfied (stepS602; NO), at step S603, the pico base station PeNB transmits a handoverrequest Nack to the macro base station MeNB. Alternatively, whendetermination is made on the basis of time-out on the macro base stationMeNB side, the pico base station PeNB may not transmit anything to themacro base station MeNB.

On the other hand, when it is decided that the admission condition issatisfied (step S602; YES), at step S604, the pico base station PeNBdecides whether the handover request received at step S601 includeshigh-speed movement information. Note that, when the high-speed movementinformation is configured of multiple bits, the radio terminal UE ismoving at a high speed may be decided by translating the contents of thehigh-speed movement information.

When it is decided that the movement speed information received at stepS601 does not include high-speed movement information (step S604; NO),at step S605, the pico base station PeNB transmits the handover requestAck to the macro base station MeNB.

On the other hand, when it is decided that the handover request receivedat step S601 includes high-speed movement information (step S604; YES),at step S603, the pico base station PeNB transmits the handover requestNack to the macro base station MeNB. Alternatively, when decision ismade on the basis of time-out on the macro base station MeNB side, thepico base station PeNB may not transmit anything to the macro basestation MeNB.

As described above, according to the fifth embodiment, when the movementspeed of the radio terminal UE is a high speed, the macro base stationMeNB notifies the pico base station PeNB of that that the movement speedof the radio terminal UE is a high speed by using the handover request.When it is notified that the movement speed of the radio terminal UE isa high speed, the pico base station PeNB rejects the handover request.Thus, the handover to the pico base station PeNB can be avoided andunnecessary handover in the heterogeneous network can be prevented.

Also, according to the fifth embodiment, the macro base station MeNBnotifies the pico base station PeNB that the movement speed of the radioterminal UE is a high speed and, thereafter, instructs the radioterminal UE to halt the processing for the measurement on the pico basestation PeNB. This can prevent a similar measurement report from beingrepeatedly generated and can decrease the overhead.

Sixth Embodiment

In the sixth embodiment, the admission decision processing (step S6 inFIG. 6) in the above-described handover procedures is improved.

Referring back to FIG. 4, an operation of a pico base station PeNBaccording to the sixth embodiment is described.

As shown in FIG. 4, a network communication unit 320 of the pico basestation PeNB according to the sixth embodiment corresponds to a receiverconfigured to receive the handover request for requesting an admissionof a radio terminal UE from a neighboring base station. The handoverrequest includes identification information on the radio terminal UE.

Also, when the network communication unit 320 receives the handoverrequest from the neighboring base station, the controller 340 of thepico base station PeNB requests the core network EPC for movement speedinformation indicating a movement speed of the radio terminal UE, andacquires the movement speed information from the core network EPC. Forexample, the mobility management device MME included in the core networkEPC manages the number of handovers/the number of cell reselections perunit time of the radio terminal UE. Thus, movement speed information canbe obtained from that information. Alternatively, when a locationinformation management device to manage information on a currentlocation of the radio terminal UE is provided in the core network EPC,the movement speed information can be obtained from information which ismanaged by the location information management device.

The controller 340 decides whether the acquired movement speedinformation indicates high-speed movement. The controller 340 controlsthe network communication unit 320 so as to transmit the handoverrequest Ack to a transmission source of the handover request when it isdecided that the movement speed information does not indicate high-speedmovement and another admission condition is satisfied.

On the other hand, in a case where another admission condition issatisfied but the movement speed information indicates high-speedmovement, the controller 340 performs control of terminating thetransmission of the handover request Ack and of not responding to thehandover request or transmitting the handover request Nack.

In this manner, in the sixth embodiment, the network communication unit320 and the controller 340 correspond to transmitters configured totransmit the handover request Ack or the handover request Nack.

Next, referring to FIG. 14, admission decision processing according tothe sixth embodiment is described. FIG. 14 is a flowchart of theadmission decision processing according to the sixth embodiment.

As shown in FIG. 14, at step S611, the pico base station PeNB receives ahandover request from the macro base station MeNB.

At step S612, the pico base station PeNB decides whether the handoverrequest received at step S611 satisfies an admission condition.

When it is decided that the admission condition is not satisfied (stepS612; NO), at step S613, the pico base station PeNB transmits thehandover request Nack to the macro base station MeNB. Alternatively,when decision is made on the basis of time-out on the macro base stationMeNB side, the pico base station PeNB may not transmit anything to themacro base station MeNB.

On the other hand, when it is decided that the admission condition issatisfied (step S612; YES), at step S614, the pico base station PeNBinquires the network EPC about the movement speed information of theradio terminal UE by using the identification information of the radioterminal UE included in the handover request received at step S611.

At step S615, the pico base station PeNB acquires the movement speedinformation obtained by the inquiry at step S614.

At step S616, the pico base station PeNB decides whether the movementspeed information acquired at step S615 indicates high-speed movement.

When it is decided that the movement speed information acquired at stepS615 does not indicate high-speed movement (step S616; NO), at stepS617, the pico base station PeNB transmits the handover request Ack tothe macro base station MeNB.

On the other hand, when it is decided that the movement speedinformation acquired at step S615 indicates high-speed movement (stepS616; YES), at step S613, the pico base station PeNB transmits thehandover request Nack to the macro base station MeNB. Or, when decisionis made on the basis of time-out on the macro base station MeNB side,the pico base station PeNB may not transmit anything to the macro basestation MeNB.

As described above, according to the sixth embodiment, when receivingthe handover request, the pico base station PeNB acquires movement speedinformation of the radio terminal UE from the core network EPC. When theacquired movement speed information indicates high-speed movement, thepico base station PeNB rejects the handover request, so that thehandover to the pico base station PeNB can be avoided and unnecessaryhandover in the heterogeneous network can be prevented.

Seventh Embodiment

In the seventh embodiment the measurement processing (step S2 in FIG. 6)in the above-described handover procedures is improved.

Referring back to FIG. 3, an operation of a radio terminal UE accordingto the seventh embodiment is described.

As shown in FIG. 3, a controller 260 of the radio terminal UE accordingto the seventh embodiment corresponds to a measurement unit configuredto perform measurement according to a parameter included in themeasurement configuration which is received by the radio communicationunit 210.

Also, the controller 260 corresponds to an acquisition unit configuredto acquire movement speed information indicating a movement speed of theradio terminal UE. A method of acquiring the movement speed informationis similar to that of the first embodiment.

Furthermore, the controller 260 controls the radio communication unit210 so as to transmit a measurement report including measurementinformation on a measurement result of the macro base station MeNB. Themeasurement information is configured by associating the measurementresult (RSRP/RSRQ) with a measurement ID of a base station (a cell) as ameasurement target. In the seventh embodiment, the radio communicationunit 210 and the controller 260 correspond to reporting units configuredto report the measurement information to the macro base station MeNB.

When the measurement result of the pico base station PeNB is obtainedand the obtained movement speed information indicates high-speedmovement, the controller 260 performs control so that a measurementreport from which the measurement information on the measurement resultof the pico base station PeNB is excluded is transmitted. In a casewhere, with the measurement, a measurement result 1 is obtained for ameasurement ID of a macro base station MeNB′ and a measurement result 2is obtained for a measurement ID of the pico base station PeNB, themeasurement report is transmitted without including the measurementinformation for the pico base station PeNB (the measurement ID and themeasurement result 2), but including the measurement information for themacro base station MeNB′ (the measurement ID and the measurement result1).

Next, referring to FIG. 15, measurement processing according to theseventh embodiment is described. FIG. 15 is a flowchart of measurementprocessing according to the seventh embodiment.

As shown in FIG. 15, at step S241, the radio terminal UE receives ameasurement configuration.

At step S242, the radio terminal UE measures RSRP/RSRQ of a measurementtarget base station (a measurement target cell) which is designated by aparameter which is included in the measurement configuration.

At step S243, the radio terminal UE decides whether the measurementresult obtained at step S242 includes a measurement result of the picobase station PeNB.

When it is decided that the measurement result of the pico base stationPeNB is not included (step S243; NO), at step 244, the radio terminal UEperforms measurement report decision and transmission processing asusual.

On the other hand, when it is decided that the measurement result of thepico base station PeNB is included (step S243; YES), at step S245, theradio terminal UE acquires movement speed information indicating amovement speed of the radio terminal UE.

At step S246, the radio terminal UE decides whether the movement speedinformation acquired at step S245 indicates high-speed movement.

When it is decided that the movement speed information acquired at stepS246 does not indicate high-speed movement (step S246; NO), at step 244,the radio terminal UE performs measurement report decision andtransmission processing as usual.

On the other hand, when it is decided that the movement speedinformation acquired at step S246 indicates high-speed movement (stepS246; YES), at step S247, the radio terminal UE transmits themeasurement Report from which the measurement information on themeasurement result of the pico base station PeNB is excluded to themacro base station MeNB.

As described above, according to the seventh embodiment, the radioterminal UE moving a high speed does not to report the measurementinformation on the pico base station PeNB to the macro base stationMeNB. Thus, the handover to the pico base station PeNB can be avoidedand unnecessary handover in the heterogeneous network can be prevented.

Eighth Embodiment

In the eighth embodiment, the handover decision processing (step S4 inFIG. 6) in the above-described handover procedures is improved.

Referring back to FIG. 2, an operation of a macro base station MeNBaccording to the eighth embodiment is described.

As shown in FIG. 2, a radio communication unit 110 of the macro basestation MeNB according to the eighth embodiment corresponds to areceiver configured to receive a measurement report from a radioterminal UE.

Also, a controller 140 of the macro base station MeNB corresponds to anacquisition unit configured to acquire movement speed informationindicating a movement speed of the radio terminal UE. A method ofacquiring the movement speed information is similar to that of the thirdembodiment.

Also, the controller 140 decides whether the measurement report which isreceived by the radio communication unit 110 includes measurementinformation (a measurement ID and a measurement result) on a pico basestation PeNB.

Furthermore, the controller 140 corresponds to a decision unitconfigured to decide a handover target of the radio terminal UE on thebasis of the measurement report which is received by the radiocommunication unit 110. When the acquired movement speed informationindicates high-speed movement and the measurement report includes themeasurement information on the pico base station PeNB, the controller140 decides a handover target of the radio terminal UE after excludingthe measurement information on the pico base station PeNB from themeasurement report. In other words, when the acquired movement speedinformation indicates high-speed movement, the handover target of theradio terminal UE is decided without considering the measurementinformation on the pico base station PeNB.

Next, referring to FIG. 16, handover decision processing according tothe eighth embodiment is described. FIG. 16 is a flowchart of handoverdecision processing according to the eighth embodiment.

As shown in FIG. 16, at step S421, the macro base station MeNB receivesa measurement report from the radio terminal UE.

At step S422, the macro base station MeNB decides whether themeasurement report received at step S421 includes the measurementinformation on the pico base station PeNB.

When it is decided that the measurement report does not include themeasurement information on the pico base station PeNB (step S422; NO),at step S426, the macro base station MeNB performs normal handovertarget decision processing, that is, processing similar to theabove-described handover procedures.

On the other hand, when it is decided that the measurement reportincludes the measurement information on the pico base station PeNB (stepS422; YES), at step S423, the macro base station MeNB acquires movementspeed information indicating a movement speed of the radio terminal UE.

At step S424, the macro base station MeNB decides whether the movementspeed information acquired at step S423 indicates high-speed movement.

When it is decided that the movement speed information does not indicatehigh-speed movement (step S424; NO), at step S426, the macro basestation MeNB performs normal handover target decision processing.

On the other hand, when it is decided that the movement speedinformation indicates high-speed movement (step S424; YES), at stepS425, the macro base station MeNB excludes (deletes) the measurementinformation on the pico base station PeNB from the measurement report.After that, at step S426, the handover target of the radio terminal UEis decided.

As described above, according to the eighth embodiment, when the radioterminal UE is moving at a high speed and the measurement report fromthe radio terminal UE includes the measurement information on the picobase station PeNB, the macro base station MeNB excludes the measurementinformation on the pico base station PeNB from the measurement reportand decides the handover target of the radio terminal UE. Thus, thehandover to the pico base station PeNB can be avoided and unnecessaryhandover in the heterogeneous network can be prevented.

Other Embodiments

As described above, the present invention has been described by usingthe above-described embodiments. However, it should not be understoodthat the description and the drawings, which constitute one part of thisdisclosure, are to limit the present invention. Various alternativeembodiments, examples, and operational techniques will be obvious forthose who are in the art from this disclosure.

In the above-described embodiments, the description is mainly given tohandover in which a radio terminal UE in a connected state switches basestations. However, the first and second embodiments may be employed in acell reselection.

FIG. 17 is an operational sequence diagram of an operation of a radioterminal UE in an idle state reselecting a cell from a macro basestation MeNB to a pico base station PeNB.

As shown in FIG. 17, at step S11, the macro base station MeNB broadcastsa system information block (SIB) which is broadcast informationincluding a cell reselection parameter.

At step S12, the radio terminal UE performs measurement processingaccording to the cell reselection parameter included in the receivedSIB.

At step S13, the radio terminal UE switches a base station connected forstand-by (a cell connected for stand-by) according to the cellreselection parameter included in the received SIB.

FIG. 18 is an operational flowchart of the macro base station MeNB whenthe first embodiment is employed in the cell reselection.

As shown in FIG. 18, at step S111, the macro base station MeNB transmitsSIB including cell reselection parameters for respective movementspeeds. Here, the cell reselection parameter for high-speed movement isconfigured to inhibit a cell reselection to the pico base station PeNB.

FIG. 19 is an operational flowchart of the radio terminal UE when thefirst embodiment is applied to the cell reselection.

As shown in FIG. 19, at step S211, the radio terminal UE receives theSIB including the cell reselection parameters for respective movementspeeds.

At step S212, the radio terminal UE acquires the movement speedinformation indicating a movement speed of the radio terminal UE.

At step S213, the radio terminal UE selects a cell reselection parametercorresponding to the movement speed information acquired at step S212from the cell reselection parameters for respective movement speedsreceived at step S211.

At step S214, the radio terminal UE measures RSRP/RSRQ of a measurementtarget base station (a measurement target cell) which is designated bythe cell reselection parameter selected at step S213.

At step S215, the radio terminal UE decides whether the measurementresult obtained at step S214 satisfies a cell reselection conditionwhich is designated by the cell reselection parameter selected at stepS213.

When it is decided that the cell reselection condition is satisfied(step S215; YES), at step S216, the radio terminal UE executes the cellreselection.

As described above, by employing the first embodiment in the cellreselection, cell reselection to the pico base station PeNB by the radioterminal UE moving at a high speed can be avoided and an unnecessarycell reselection in the heterogeneous network can be prevented.

FIG. 20 is an operational flowchart of the radio terminal UE when thesecond embodiment is employed in the cell reselection.

As shown in FIG. 20, at step S231, the radio terminal UE receives SIBincluding cell reselection parameters.

At step S232, the radio terminal UE acquires movement speed informationindicating a movement speed of the radio terminal UE.

At step S233, the radio terminal UE decides whether the movement speedinformation acquired at step S232 indicates high-speed movement.

When it is decided that the movement speed information acquired at stepS232 indicates high-speed movement (step S233; YES), at step S234, theradio terminal UE adjusts a cell reselection parameter received at stepS231 so as to inhibit the cell reselection to the pico base stationPeNB. On the other hand, when it is decided that the movement speedinformation acquired at step S232 does not indicate high-speed movement(step S233; NO), the radio terminal UE can proceed to step S235.

At step S235, the radio terminal UE measures RSRP/RSRQ of a measurementtarget base station (a measurement target cell) which is designated bythe cell reselection parameter.

At step S236, the radio terminal UE decides whether the measurementresult obtained at step S235 satisfies the cell reselection conditionwhich is designated by the cell reselection parameter.

When it is decided that the cell reselection condition is satisfied(step S236; YES), at step S237, the radio terminal UE executes the cellreselection.

As described above, by employing the second embodiment in the cellreselection, cell reselection to the pico base station PeNB by the radioterminal UE moving at a high speed can be avoided and an unnecessarycell reselection in the heterogeneous network can be prevented.

Note that, in the first to the eighth embodiments, the description isgiven with a pico base station which is a type of a low-power basestation as an example. However, not only the pico base station but alsoa femto base station (also referred to as a home base station) which isa base station forming a cell smaller than a cell formed by the picobase station or a relay node which is abase station wirelessly forming abackhaul may be set as a low-power base station according to the presentinvention.

Thus it should be understood that the present invention includes variousembodiments not described herein.

What is claimed is:
 1. A mobile communication method used for a handovercontrol in a heterogeneous network, comprising the steps of:transmitting, by a base station connected to a radio terminal, ameasurement configuration that configures an event-trigger-typemeasurement report, to the radio terminal; receiving, by the radioterminal, the measurement configuration from the base station; andtransmitting a measurement report from the radio terminal to the basestation when a report condition corresponding to the measurementconfiguration is satisfied, wherein the measurement configurationcomprises: a first report condition parameter configured to impose astrict report condition on a small cell out of cells to be measured bythe radio terminal; and a second report condition parameter configurednot to impose the strict report condition on the small cell.
 2. A radioterminal that performs a handover in a heterogeneous network,comprising: a receiver that receives a measurement configuration thatconfigures an event-trigger-type measurement report, from a base stationconnected to the radio terminal; and a controller that transmits ameasurement report to the base station when a report conditioncorresponding to the measurement configuration is satisfied, wherein themeasurement configuration comprises: a first report condition parameterconfigured to impose a strict report condition on a small cell out ofcells to be measured by the radio terminal; and a second reportcondition parameter configured not to impose the strict report conditionon the small cell.
 3. A base station that performs a handover control ina heterogeneous network, comprising: a transmitter that transmits ameasurement configuration that configures an event-trigger-typemeasurement report, to a radio terminal connected to the base station;and a receiver that receives a measurement report from the radioterminal when a report condition corresponding to the measurementconfiguration is satisfied in the radio terminal, wherein themeasurement configuration comprises: a first report condition parameterconfigured to impose a strict report condition on a small cell out ofcells to be measured by the radio terminal; and a second reportcondition parameter configured not to impose the strict report conditionon the small cell.